The long-term goals of the project described here are to use endogenous membrane transporters to target drugs and enhance delivery to specific cells. A method will be developed for prediction of substrate interaction with a transporter, and a thorough analysis of the structural requirements for substrate transport will allow synthesis of designer drugs that can be concentrated in target tissues with high specificity. This five year project has the following specific aims: i) Investigate the transport properties of a series of glucose analogs on the Na+/glucose cotransporter (SGLT1) by performing a detailed analysis of transport/binding. Compounds glycosidically linked to glucose will be the first group studied. A prodrug strategy can be integrated into this system by using endogenous glycosidases to cleave an active drug from a sugar carrier; 2) Develop a model of structural requirements for transport by combining an analysis of substrate transportability with structural data from published crystallographic structures and from sophisticated computer modeling of compounds for which structures are not known. A core, such as a glycosidic phenyl group, will be used as a framework to probe the effect on transport by different structural elements (-OH, -NO2, -CH3, etc.) added to the ring at different positions. Compounds will be screened electrophysiologically to determine whether they are transported by the Na+/glucose cotransporter (SGLT1) in Xenopus oocytes. Nontransported compounds will be assayed using radioactive tracers to determine if they are inhibitors. kinetic analysis will be performed to determine the Km for each transported substrate. Conformational analysis on these compounds will be performed using computational chemistry methods. Substrate interaction and structure will be analyzed using a 3-D QSAR to predict the interactions between substrate and the transporter. This will result in a model of the structural limits of glycosidic substituents for transport by SGLT1, increase the basic understanding of membrane transport and be the first step in the development of designer drugs targeted to specific transport proteins; 3) This method will be directly applied to other membrane transporters, such as the Na+/nucleoside and Na+/myo-inositol transporters, to explore different classes of pharmaceuticals and cellular distributions.